In addition to the known computer tomography, x-ray projections disposed on a circle can be recorded with the aid of C-arm x-ray devices and used for a tomography reconstruction. Since flat panel detectors with a maximum size of 30×40 cm are generally used here, the size of the flat panel detector thus represented a limitation in the past. This was solved in that the movement of the C-arm in novel C-arm x-ray devices takes place by means of an industrial robot. New and also complicated recording movements are herewith possible, e.g. the so-called Large Volume Acquisition. The C-arm is herewith rotated twice about the examination object, once so that the perpendicular bisector of the side is moved by the x-ray detector onto the x-ray detector to a plane running toward the x-ray source and containing the axis of rotation and a second time so that the perpendicular bisector of the side is shifted to the right relative to the plane. The projections, in which the x-ray source is located at the same location, are then merged for reconstruction purposes to form a large virtual projection. The plurality of virtual projections is then used with a standard reconstruction method, like the filtered back projection, for volume calculation purposes.
To achieve a minimal scanning time and apply as small an x-ray dose as possible, rotations of less than 360° are frequently (easily) implemented. As a minimal scanning range per rotation (in total displaced once to the left and once to the right) projections are recorded in an angular range of 180°+ fan angle of the virtual x-ray detector (combination of the x-ray detector in the position displaced to the left and the position displaced to the right) in relation to the x-ray source.
From the article by G. Wang: “X-ray micro-CT with a displaced detector array”, Med. Phys. 29 (7), pp. 1634-1636, July 2002, it is known that an increase in the measurement field can also be achieved if an x-ray detector displaced by less than 50% to the side is rotated in an angular range of 360° once about the examination object. The applied x-ray dose can as a result likewise be reduced. This method requires, however, that the x-ray device can record through 360° when the x-ray detector is displaced, which—despite all the flexibility of an industrial robot—is frequently not the case, in particular where patients are involved.